1. Field of the Invention
The present invention relates to a communication network control system and, more particularly, to a flow control in a packet exchange for switching an IP (Internet Protocol) packet in the downward direction transmitted from the Internet to a mobile terminal.
2. Description of Related Art
Current communication networks include not only a conventional wire communication network using metallic line or optical fiber but also a communication network such as a mobile communication network using radio as media of signal transmission. The mobile communication network includes:
(1) a PDC (Personal Digital Cellular) for transmitting a signal in a time slot in a manner similar to an existing STM (Synchronous Transfer Mode) communication network (a time division communication network for transmitting a signal in time slots which are time-divided in synchronized frames as described in p. 29-30 of xe2x80x9cEasy-to-understand digital exchangexe2x80x9d issued by The Telecommunications Association) as described in p. 217-251 and 301-326 in xe2x80x9cMobile Communication Handbookxe2x80x9d issued by Ohm-sha;
(2) a PHS (Personal Handyphone System) communication network; and
(3) a CDMA (Code Division Multiple Access) communication network for modulating a signal by using a code different according to each signal and transmitting the modulated signal as described in p. 32-36 in xe2x80x9cEasy-to-understand Digital Mobile Communicationxe2x80x9d issued by The Telecommunications Association.
Among them, a wide band CDMA (W-CDMA) described from page 85 in xe2x80x9cNikkei Electronicsxe2x80x9d, No. 680 issued by Nikkei BP Co. is a communication network which is expected to be a communication system capable of transmitting and receiving signals of various kinds and speeds such as voice, image, and high-speed data with quality similar to that of the existing wire communication network even if the user terminal moves at high speed. The communication network is expected to be rapidly introduced in future.
On the other hand, current communication networks include various communication networks such as: the STM communication network; a packet communication network for transmitting a signal on a variable length packet, described in p. 128-133 in xe2x80x9cBasic knowledge of data transferxe2x80x9d issued by The Telecommunications Association; an ATM (Asynchronous Transfer Mode) communication network for transmitting a signal on a fixed length packet called a cell, described in p. 64-79 in xe2x80x9cB-ISDN textbook with picturesxe2x80x9d issued by Ohm-sha; and the IP network (Internet) for transmitting an IP packet in accordance with the procedure called the Internet protocol (IP) by sending a signal on a variable length packet called an IP packet described in p. 98-103 10 in xe2x80x9cMastering TCP/IP, Introductionxe2x80x9d issued by Ohm-sha. In each of the communication networks, media of voice, image and data are transmitted/received.
In recent years, a mobile packet network such as the Internet and a PDC-P (PDC-Packet) has been greatly introduced. In the Internet protocol (refer to RFC791, as per Internet Engineering Task Force) used on the Internet as a de facto standard communication protocol in the packet communication, controlling of a communication bandwidth of data or the like has not been examined in consideration of a data flow. That is, the most primitive method of transmitting data as much as possible unless a transmission path is congested in accordance with the order of arrival of data and transmitting no data when the transmission path is congested is used.
The method has a problem that a data flow of data such as a moving picture which should not be delayed but may be dropped a little and a data flow of data such as an electronic mail which may be delayed but should be complete cannot be dealt separately. In other words, the characteristic of the data flow is ignored. Especially, at the time of congestion, the problem is fatal. When data is not dealt according to the characteristic of the data flow, data to be preferentially sent when the transmission path is congested cannot be determined. An unpreferable situation such that an electronic mail which may be delayed is transmitted before a moving picture which should not be delayed can occur.
It is therefore considered that improvement on this point will be necessary in future by, for example, allocating a bandwidth to transmission of moving pictures wider than that of electronic mail so as to transmit the moving picture first. In the communication network in the next generation, it is presumed that a QoS (Quality of Service) control such as a control on a data transmission bandwidth is an important technique.
The Internet, however, originally lacks a function of supporting a mobile terminal on the network side. In the case of transmitting the IP packet from a fixed terminal on the Internet side to a mobile terminal on a mobile communication network side, especially, the fixed terminal performs a packet transmission without considering whether the data flow is for a mobile terminal or not.
A wireless access network peculiar to the mobile communication network positioning between a mobile terminal and a subscriber exchange on the mobile communication network side accommodates a number of mobile terminals and the bandwidth in the radio zone is narrow. Consequently, an upper limit is set so that the bandwidth in the wire zone allocated to each IP data flow does not exceed the channel bandwidth in the radio zone.
In order to prevent occurrence of an overflow of data in a wireless base station or the like for performing interwork between the wire zone and the radio zone, in the subscriber exchange on the mobile communication network side, it is necessary to perform a flow control (an example of the QoS control) on the flow of data entering from the Internet in the downward direction, of which bandwidth is not limited.
A specification required for the packet exchange service in the mobile communication network is being formed by including the flow control for each data flow in the downward direction. As an example, various service requirements are defined in documents in the IMT-2000 system based on the GPRS method (ETSI: GSM 03.60 Stage 2 Service Description of the General Packet Radio Service (GPRS)). The QoS control includes a bandwidth control, a delay control, a priority control, and a reliability control. It is presumed that the importance of the QoS control system for each data flow of a packet transmitted from a fixed terminal on the Internet side to the mobile terminal on the IMT-2000 system will be increased with the spread of the mobile packet communication in future.
As mentioned above, the flow control for the conventional IP data flow is performed by adjusting the traffic amount. Specifically, traffic of the IP data flow is actually measured by an intermediate exchange. When the traffic amount tends to increase, a radio channel is switched to a channel of a wider bandwidth and, simultaneously, an increase in the flow in the wire zone is permitted within the radio resources allowable range. The traffic which can be measured by the intermediate exchange is classified into effective traffic to be actually flowed and retransmission traffic occurring in association with degradation in the communication quality in the radio zone or the like.
Since the packet is encrypted and compressed in the mobile communication network, when the retransmission traffic increases, it is very difficult to distinguish between the retransmission traffic and the effective traffic in the intermediate exchange. Consequently, the exchange regards that the traffic of the IP data flow sent from the Internet increases.
As described above, when an ordinary flow control is executed on the basis of only the measured traffic amount, in the conventional flow control system for permitting the increase in traffic entering from the Internet side, a data loss frequently occurs in an apparatus such as a wireless base station having a small buffer capacity. As a result, the retransmission traffic further increases and the data loss more frequently occurs.
In order to solve the problem, it is necessary to execute the flow control by using the radio communication quality information, communication quality information classified into retransmission traffic and effective traffic, and traffic amount information.
An object of the invention is to provide a communication control system in a mobile communication network which is connected to the Internet and realizes the IP packet switching, including: (1) a unit for efficiently measuring a traffic amount of each data flow by an intermediate exchange; and (2) a practical flow control unit based on communication quality information in a radio zone provided by a wireless base station, communication quality information of, each of data flow classified into retransmission traffic and effective traffic provided by a subscriber exchange, and a traffic amount of each data flow measured by a base station controller.
The communication control system according to the invention operates as follows. The wireless base station converts radio quality information carried on a data frame in the upward direction transmitted from a mobile terminal to the wireless base station into a data format used in the wire zone and notifies a base station controller of the converted information. A traffic monitor measures the traffic amount of the data frame in the downward direction transmitted from a subscriber exchange to a mobile terminal classifying into the retransmission traffic amount and the effective traffic amount for each data flow. The subscriber exchange collects the communication quality information for each data flow and notifies a traffic controller of the collected information.
The base station controller determines whether the radio channel has to be switched or not generally from the traffic amount in the downward direction of each measured data flow, the communication quality in the radio zone, and the communication quality of each data flow between the mobile terminal and the subscriber exchange.
When it is determined that the radio channel has to be switched, the base station controller switches the data channel of the mobile terminal and the wireless base station. After switching the channel, the subscriber exchange executes the flow control in the downward direction. When the communication quality in the radio zone and the communication quality between the mobile terminal and the subscriber exchange are preferable and an increase in the data flow in the downward direction is observed, the flow control in the downward direction is carried out by promptly increasing the bandwidth of the data flow in the downward direction in the subscriber exchange.
A process in a case where degradation in the communication quality is reported is performed as follows. The factors requiring a report of the degradation in the communication quality in the radio zone to the subscriber exchange include (1) power down or failure in the mobile terminal, (2) degradation in a radio wave state, and (3) power down or failure in the wireless base station. In the cases of (1) and (2), the radio communication quality or air quality information of each terminal is reported to the radio base controller. In the case of (2), since the radio communication quality information is not reported to the base station controller for a certain period, it is regarded that the radio communication quality information of all of terminals deteriorates.
The factors requiring a report of the degradation in the communication quality between the mobile terminal and the subscriber exchange include (1) a data loss caused in association with the power down, failure, or movement of the mobile terminal, (2) degradation in the radio wave state, (3) power down, failure, or the like of the wireless base station, and (4) buffer overflow on the subscriber exchange side.
As described above, there is the high correlation between the communication quality information between the mobile terminal and the subscriber exchange and the communication quality information in the radio zone. The degradation in the communication quality due to an increase in the retransmission traffic caused by a data loss which occurs when the communication is temporarily interrupted in association with roaming does not depend on the communication quality in the radio zone. In the mobile packet communication system in which a perfect handover mechanism has not been realized, the data loss due to the movement occurs the most and is measured as degradation in the communication quality in the subscriber exchange.
The degradation in the communication quality which occurs in association with the roaming can be measured by the base station controller from the radio communication quality information sent from the wireless base station and the communication quality information sent from the subscriber exchange at the same time. To be specific, when the degradation in the communication quality is reported from the subscriber exchange and no degradation in the radio communication quality is reported from the wireless base station, it may be determined that the data loss in association with the roaming has occurred, and a signal to start the flow control process is sent also to the subscriber exchange. In this case, it is desirable to temporarily interrupt the data transmission.
If the flow control in the downward direction is determined by the subscriber exchange, it is necessary to collect the radio communication quality information from all of wireless base stations under the subscriber exchange. In this case, not only the traffic of signals passing through the line is increased but also a processing load on the subscriber exchange side increases. It is the most efficient, therefore, that the base station controller starts a channel switching process and a flow control process. By sharing and performing the channel switching process and the flow control process by the base station controllers, a well-balanced communication control system having the high practicability can be constructed.